A conventional CMP machine includes a rotating polishing pad, a wafer carrier and a conditioning disk with an abrasive surface used to condition the polishing pad. During CMP processing, a liquid slurry of abrasive particles is poured onto the rotating polishing pad and a semiconductor wafer is placed in the wafer carrier. The wafer carrier presses the wafer against the slurry and the rotating polishing pad while the carrier moves the wafer across the width of the polishing pad. The chemical reaction with the slurry and the physical erosion due to the contact with the abrasive particles causes material to be removed from the wafer and evens out any irregular topography, making the exposed wafer surface planar. The conditioning disk includes an abrasive surface and is coupled to an arm that rotates the conditioning disk and sweeps the conditioning disk abrasive surface against the polishing pad surface. The conditioning disk keeps the particles removed from the wafer from accumulating on the polishing pad surface and maintains the uniform abrasive character of the polishing pad.
In a normal CMP system, the conditioning disk actuator applies a constant compressive force to press the conditioning disk against the polishing pad. The conditioning disk also rotates at a constant rate of rotation and the conditioning disk is moved across the radius of the polishing pad at a constant sweep rate. When a new polishing pad and a new conditioning disk are installed in a CMP machine, the abrasive surface of the conditioning tends to be very sharp and the rate of material removal from the polishing pad is initially high. During the life of the conditioning disk, the abrasive surface is worn down and the sharpness of the conditioning disk is reduced. This causes the rate of material removal to be reduced as the conditioning disk is used. Thus, in a prior art CMP machine, the rate of material removal is not controlled and the rate of material removal from the polishing pad is not linear throughout the life of a polishing pad. Accordingly, what is needed is a CMP control system that monitors the status of the conditioning disk and adjusts the rate of material removal to optimize the life of the polishing pad.